A fluid, typically methanol, is injected into natural gas wells to prevent freezing in extremely cold environments such as winter in Northern Canada. Freeze protection is accomplished with relatively little methanol if it is injected at regular intervals. Because electricity is not available at the remote locations of wellheads, the pressure of natural gas in the well is used to drive an injection pump that controls introduction of methanol (from a pressurized supply) into the natural gas pipe line.
For example, the model BR5000 Chemical Injector Pump (Bruin Instruments Corp., Edmonton, Alberta, Canada) is a single acting, positive displacement plunger type pump. The pump is powered with air or other gas pressure (50 psig-maximum) acting on a diaphragm, resulting in plunger displacement. When full stroke (1¼″ inch) is reached, the internal switching system of the pump shuts off the supply gas (for example, natural gas used to power the pump) and vents the diaphragm chamber. The diaphragm is equipped with a return spring for retracting the plunger. The internal switching system toggles, for example, a micro switch to shut off the supply gas and vent the diaphragm chamber. A similar pump from the same manufacturer is the model 5100, which is powered by gas pressure as low as 8 psig (maximum 35 psig) and has a full stroke of one inch.
Current pump design is such that the injection pump cannot be operated reliably at very low stroke rates without losing the assurance that the pump has not hung-up in mid-stroke, thus failing to accomplish the desired injection of methanol. Because wellheads are in very remote locations, and are not actively monitored (due in large part to the lack of electricity to power monitoring equipment), the only viable option today is to operate the injection pumps at relatively high stroke speeds to ensure that they operate properly. The downside of high stroke speeds is high consumption of the natural gas used to power the pumps. This results in an environmental problem, as well as a financial problem, due to venting of natural gas to the atmosphere. Initially, the natural gas is used to displace the pump plunger and thereby inject methanol into the well. After the gas is used to displace the plunger, it is vented. It is vented because after gas expansion during displacement of the plunger, the gas has too little pressure to be captured and transported cost-effectively.